Reinforced flexible hose

ABSTRACT

A reinforced flexible hose includes at least one inner tubular layer ( 2 ) of plastic or rubber, a knitted reinforcement ( 3 ), which has substantially , parallel rows ( 4 ) and lines ( 5 ) of substantially parallel stitches, with respective stitch counts per unit length of the hose (Nm, Nr); and an outer layer ( 6 ) which is superimposed on the reinforcement layer ( 3 ) to protect it. The knitted reinforcement layer ( 3 ) is provided in the form of a single tubular layer and is wrapped around the outer surface of the inner tubular layer ( 2 ); the rows ( 4 ) and lines ( 5 ) of stitches are substantially helical, with respective longitudinal pitches (P m , P r ) and inclinations which are mutually opposite with respect to the longitudinal axis (Y). The longitudinal pitch 2 (P r ) of the lines ( 5 ) of stitches is substantially proportional to the square of the outside diameter (φ o ) of the inner layer ( 2 ), whilst the number of lines (N r ) of stitches per unit length of the hose is directly proportional to the outside diameter (φ o ) of the inner layer ( 2 ).

The present invention relates to a flexible hose made of plastic orreinforced rubber, with a tubular braiding made of fabric which can beused in the field of irrigation or in the field of the delivery ofpressurized fluids in open or closed circuits.

Conventional flexible hoses of the above described type are generallyformed by a first tubular inner layer, made of plastic or rubber, onwhich a tubular fabric is applied for increasing the pressure resistanceof the flexible hose, reducing its deformation and increasing itsperformance.

One of the most widespread and most suitable conventional hose is theso-called “mesh-reinforced” type, in which the tubular reinforcementfabric is constituted by a series of threads spirally wound on theflexible hose in parallel and equidistant rows and superimposed on anequal number of transverse threads along likewise parallel andequidistant lines which are arranged symmetrically with respect to theaxis of the hose so as to form a mesh with diamond-shaped cells.

The fabric surrounding the outer surface of the inner layer of plasticis then covered by a further outer layer of plastic or rubber which isgenerally but not necessarily transparent and fixes the meshed fabric tothe flexible hose and protects it. With this type of braiding, theflexible hose is suitable to withstand a higher pressure than the hosewithout braiding and to reduce its deformation, because the weaving isof the non-stretch type and therefore prevents the inner layer fromdeforming.

A drawback of the above described mesh-reinforced hose is the fact thatits flexibility is relatively limited; that is to say, the bendingradiuses to which the hose can be subjected are rather wide with respectto knit hoses.

Another conventional type of flexible hose is the one in which thebraiding that surrounds the outer part of the hose is formed by knittinginstead of weaving.

EP-A-0 527 512, in the name of this same Applicant, discloses a hoseprovided with a particular knit reinforcement in which the individualstitches are shaped like trapezoidal loops with filaments whichinterweave in the corners. This type of knit reinforcement has thevirtue of making the hose stronger than similar knit flexible hoses.

It is known that knitting is a special weaving which is obtained bymeans of one or more threads which are mutually linked with more or lesscomplex turns, also known as loops or basic stitches, which give theknit fabric great elasticity.

So-called chain knitting is constituted by a series of mutually parallelthreads which are fed by multiple spools and are curved so as to form anequal number of lines of stitches which are interlocked both in the weftdirection and in the chain direction; their interweaving produces atransverse series of rows of stitches and a longitudinal series of linesof stitches or cords.

One of the commercially most frequent flexible hoses is the one in whichthe knitting is of the tricot chain type, where this term describes astitch in which each thread forms the stitch by interweaving with one ormore threads to its right and with one or more threads to its left.

Although, on one hand, the flexible hose with tricot knitting is moreflexible, since notoriously the knitting yields as the diameter of thehose increases because of the pressure increase, on the other hand theshortcoming of knitted fabric, and especially of tricot-knitted fabric,is that as the pressure increases, the hose is subjected to a torsionaleffect by the fluid which flows under pressure inside it. This is due tothe helical orientation of the rows of stitches which, by contrast withthe substantially longitudinal orientation of the lines, cause anunbalanced reaction, and particularly torque, in the hose.

EP-A-0 623 776 in the name of this same Applicant discloses a hose whichincludes, from the inside outward: an inner layer of plastic or rubberwhich has an outer surface; a chain-knit part, which has rows and linesof stitches, and has a tubular shape and is wound in a single layeraround the outer surface of the inner layer; and an outer stitchprotection layer; wherein the lines and rows of stitches are inclined inopposite directions with substantially the same inclination with respectto the longitudinal axis of the hose in order to eliminate the effectsof the torque produced by the pressure loads inside the hose.

This prior patent provides no correlation among the various parametersof the knit reinforcement part, such as the pitch, the inclination andthe thread count per unit length, neither among them or with respect tothe dimensional parameters of the inner layer. Accordingly, due to thelarge number of parameters involved and to their large number ofpossible combinations, the person skilled in the art does not have allthe information required to assuredly achieve the intended results or atleast optimize the anti-torque effect of the hose.

An aim of the present invention is to eliminate the above describeddrawbacks.

A further aim of the invention is to provide a correlation between thevarious parameters of the braiding and those of the inner layer, such asto eliminate the torque produced on the knitted fabric by the pressureof the fluid, without thereby renouncing flexibility and burstingpressure resistance characteristics.

This aim and other objects which will become apparent hereinafter areachieved by a flexible hose according to the invention, which inaccordance with the content of the first claim includes: at least oneinner tubular layer of plastic or rubber which has an outside diameterand a longitudinal axis; a knitted reinforcement of the chain type,which has rows of substantially parallel stitches and lines ofsubstantially parallel stitches with respective stitch counts per unitlength in a longitudinal direction, the knitted reinforcement layerbeing provided in the form of a single tubular layer and beingwrapped-around the outer surface of the inner tubular layer coaxiallythereto, the rows and lines of stitches being substantially helical withrespective longitudinal pitches and inclinations which are mutuallyopposite with respect to the longitudinal axis, so as to eliminate thetorque applied by the pressure of the fluid inside it; and an outerlayer which is superimposed on the reinforcement layer to protect it;characterized in that the longitudinal pitch of the lines of stitches issubstantially proportional to the square of the outside diameter of theinner layer.

Surprisingly, it has been found that in order to eliminate the torqueinduced by the internal pressure of the fluid, the pitch of the lines ofstitches must increase as the inner diameter but not according to alinear relation but rather according to a quadratic relation, in orderto effectively contrast the rotation induced by the uncoiling of thehelical threads of the stitches.

At the same time, the longitudinal pitch of the rows of stitches can bekept substantially constant and independent of the outside diameter ofthe inner layer.

Preferably, the number of lines of stitches per unit length of the hoseis directly proportional to the outside diameter of the inner layer.

Further characteristics and advantages of the present invention willbecome apparent from the following description of a preferred embodimentof the invention, illustrated only by way of non-limitative example inthe accompanying drawings, wherein:

FIG. 1 is a view of a portion of the flexible hose according to theinvention;

FIG. 2 is a sectional view of the hose of FIG. 1;

FIG. 3 is a diagram showing the main parameters of the chain knitting ofthe reinforcement braiding according to the invention with respect tothe outside diameter of the inner layer.

With reference to the above figures, the flexible hose according to theinvention, generally designated by the reference numeral 1, is formed byan inner layer 2 made of polymeric or elastomeric material such as PVC,natural or synthetic rubber, which is essentially tubular and has alongitudinal axis Y which coincides with the axis of the flexible hose,an inner surface which has an inside diameter φ_(i), and an outersurface which has a diameter φ_(o).

A chain-knitted part, generally designated by the reference numeral 3,is knitted on the inner layer 2 and is formed by substantially helicalrows 4 of stitches, which are mutually parallel and have an inclinationangle α with respect to the axis Y of the hose 10 of FIG. 2, and bylines 5 which are also substantially helical and have an inclinationangle B with respect to the axis Y, but in the opposite direction withrespect to the rows 4.

The rows and lines have respective longitudinal pitches P_(m) and P_(r).Furthermore, the linear count or number of lines per unit length (100mm) of the rows or stitches is respectively N_(m) and N_(r).

It is known that if the outside diameter φ_(o) of the inner layer 2 onwhich the braiding 3 is wound increases, it is necessary to increase thepitch of the lines in order to be able to contain the torque. However,until now a precise correlation between these parameters had not beenestablished. Surprisingly, tests and experiments have allowed to verifythat the relation between these parameters is not linear but is insteadquadratic.

In other words, this relation can be expressed by the general formula:

P _(r) =Kφ ²  (1)

where the parameter K depends on the materials and units of measureused.

In the case of PVC and if all parameters are expressed in mm, theconstant K of formula (1) is generally between 0.35 and 0.50 mm⁻¹ and ispreferably equal to approximately 0.45 mm⁻¹.

It is noted that the knitted reinforcement of the hose of FIG. 1 isformed by chain stitches of the tricot type. These stitches are formeddirectly on the hose by so-called knitting machines which arecommercially available and whose stitch-forming method is well-known.

With this crossed and inclined arrangement with respect to the axis Y ofthe hose, the torque which occurs on the hose in case of normal chainstitches, for example with substantially longitudinal lines, is canceledout. On the contrary, by arranging the lines transversely instead oflongitudinally the rotary force component which appeared due to thecoiling of the spiral-shaped rows 5 is compensated.

With this type of knitting, the forces produced by the lines and rows ofstitches mutually compensate until they cancel each other out, thusmaking the hose 1 substantially insensitive to the torque induced by thepressure of the fluid inside the hose.

It is noted instead that the longitudinal pitch P_(m) of the rows ofstitches can be kept substantially constant and independent of theoutside diameter φ_(o) of the inner layer.

Furthermore, the number N_(r) of lines of stitches per unit length ofthe hose is substantially directly proportional to the outside diameterφ_(o).

The angles α and β are generally mutually different, but their sum isapproximately constant and equal to, or slightly smaller than, 90° asthe value of the outside diameter φ_(o) of the inner layer 2 varies.

In particular, it has been observed that the inclination angle β of thelines of stitches 5 is substantially proportional to the square root ofthe outside diameter φ_(o) of the inner layer 2.

When using values between 12 and 37 mm for the outside diameter φ_(o)and between 10 and 32 mm for the inside diameter φ_(i), it has beenobserved that the number of rows per unit length N_(m) is substantiallyconstant and is between 30 and 40 rows per 100 mm, with an average valueof 35 rows per 100 mm.

In the same conditions, the number of lines per unit length N_(r) issubstantially proportional to the outside diameter φ_(o) of the innerlayer 2 and is between 10 and 16 rows per 100 mm.

Some of the above parameters have been plotted in the chart of FIG. 3.

Finally, an outer layer 6 made of plastic or rubber locks the chainknitting thus formed on the surface of the hose, as occurs besides inall known flexible hose structures.

It is important to note that the inclination of the lines and rows ofstitches can be slightly modified with respect to the above indicatedvalues according to the material of the hose, its diameter, the type ofknitting, the number of spools, the pitch of the rows and lines, and thetype and/or count of the thread.

What is claimed is:
 1. Reinforced flexible hose, comprising: at leastone inner tubular layer (2) of plastic or rubber which has an outside(φ_(e)) diameter and a longitudinal axis (Y); a chain knitted-typereinforcement layer (3), which has rows (4) of substantially parallelstitches and lines (5) of substantially parallel stitches, withrespective stitch counts per unit length (N_(m), N_(r)) in alongitudinal direction; said knitted reinforcement layer (3) beingprovided in the form of a single tubular layer and being formed on theouter surface of said inner tubular layer (2) coaxially thereto; saidrows (4) of stitches and said lines (5) of stitches being substantiallyhelical with respective longitudinal pitches (P_(m), P_(r)) andinclinations (α, β) which are mutually opposite with respect to thelongitudinal axis (Y), so as to eliminate the torque applied by-thepressure of the fluid inside it; and an outer layer (6) which issuperimposed on said reinforcement layer (3) to protect it;characterized in that the longitudinal pitch (P_(r)) of said lines (5)of stitches is substantially proportional to the square of the outsidediameter (φ_(o)) of said inner layer (2).
 2. Flexible hose according toclaim 1, characterized in that the number of lines of stitches per unitlength (N_(r)) is substantially directly proportional to the outsidediameter (φ_(o)) of said inner layer (2).
 3. Flexible hose according toclaim 1, characterized in that the longitudinal pitch (P_(m)) of therows of stitches is substantially constant and independent of theoutside diameter (φ_(o)) of said inner layer (2).
 4. Flexible hoseaccording to claim 1, characterized in that said rows (4) and said lines(5) of substantially helical stitches have different inclination angles(α, β) whose sum is substantially constant and equal to, or slightlylower than, 90° as the value of the outside diameter (φ_(o)) of saidinner layer (2) varies.
 5. Flexible hose according to claim 4,characterized in that the angle of inclination (β) of the lines (5) ofstitches is substantially proportional to the square root of the outsidediameter (φ_(o)) of said inner layer (2).
 6. Flexible hose according toclaim 1, characterized in that in said inner layer (2) the outsidediameter (φ_(o)) is between 12 and 27 mm and the inside diameter (φ_(i))is between 10 and 32 mm.
 7. Flexible hose according to claim 1,characterized in that the number of rows per unit length (N_(m)) issubstantially constant as the outside diameter (φ_(o)) of said innerlayer (2) varies, and is between 30 and 40 rows per 100 mm, with anaverage number of 35 rows per 100 mm.
 8. Flexible hose according toclaim 1, characterized in that the number of lines per unit length(N_(r)) is substantially proportional to the outside diameter (φ_(o)) ofsaid inner layer (2) and is between 10 and 16 lines per 100 mm.